Flood flow frequency estimates on the Des Moines River have increased, according to a nine-month study done by the U.S. Army Corps of Engineers.

The study looked at flow frequencies at Saylorville Lake, Lake Red Rock and Southeast Sixth Street in Des Moines. The study included a scientific assessment to estimate the frequency and magnitude of future reservoir outflows by analyzing the 14 years from 1995 to 2008.

It found that flood flow frequencies have increased above previous estimates by the Corps, and that the floods of 1993 and 2008 were more likely than previously thought.

The study re-evaluated the amount of outflow that constitutes a given probability. For example, the cubic feet per second (cfs) outflow on June 12, 2008, was 47,000, which at the time represented a 200-year flood. That number now falls under the category of a 50-year flood, which means it is four times as likely to happen.

The highest recorded outflow at Lake Red Rock was 104,500 cfs in 1993, which now constitutes a 100-year flood plain value rather than a 200-year flood plain value.

Corps officials yesterday met with representatives from the cities of Des Moines and Ottumwa, Polk and Wapello counties, the Iowa departments of Natural Resources and Transportation, the Federal Emergency Management Agency, Sen. Tom Harkin, Congressmen Leonard Boswell and Dave Loebsack and Gov. Terry Branstad.